1. Related Application
This application is related to U.S. patent application Ser. No. 867,487 filed May 27, 1986, now U.S. Pat. No. 4,759,070, entitled PATIENT CONTROLLED MASTER HEARING AID which disclosed a test apparatus for patient selection of the electronics to be incorporated into the hearing aid of this invention. The disclosure of that application is incorporated herein by reference.
2. Field of the Invention
This invention relates to the field of hearing aids, and more particularly to an in-the-canal miniaturized hearing aid which has all of its electrical and mechanical components, including a replaceable battery, contained within a prefabricated earshell assembly composed of a hollow rigid body with a soft, resilient covering fixed to the exterior.
3. Description of the Prior Art
Numerous types and designs of hearing aids for assisting persons with hearing deficiencies are known in the prior art. Typically, hearing aids incorporate a microphone for converting sound waves to electrical signals. These signals are then amplified by an amplifier circuit and sent to a receiver. The receiver converts the electrical signals into amplified sound waves and directs the sound waves toward the eardrum.
Many efforts have been made to address the tragic impairment of the hearing sense. It is believed that most of these prior contributions have assisted the patient who wore them and therefore they are important contributions. It is believed that most, however, have, while assisting in part the hearing problem, contributed other discomforts to the patient.
The majority of prior devices include a bulky protrusion from the ear, noticeable by all, indicating that the patient or user wears a hearing aid. A more recent modification relocated the controls which protruded from the ear to a position in back of the ear. Attempts to overcome the outward extending controls included the creation of custom molded in-the-canal hearing aids.
Most popular hearing aids today are very expensive and are created by this custom molding method or process by which a soft silicone or similar ear impression material is used to take an impression of the patient's ear canal which is then used to create a hard plastic shell for a hearing aid which conforms to the patient's ear. However, after the hard plastic shell is rendered from the ear impression, individual technicians at the manufacturing plant cut, buff and polish the hearing aid, often changing the configuration or mold so that it no longer is able to conform precisely to the ear from which the first impression was taken. In addition, the buffing and polishing which is done to make the aid slip into the ear becomes the surface which permits feedback of sound to occur causing an unpleasant squeal in many circumstances. For example, buffing "rough spots" generated during the ear impression process creates imperfections of the interface between the hearing aid and the inner surface of the ear. These imperfections cause "pin prick" openings which permit sound from the receiver to leak back to the microphone.
Thus, with prior custom molded hearing aids there is often a need for modifications to the device and repeated exchange between the patient and the factory. Since the components are normally glued together, the replaced hearing aid must again be constructed using the same or similar process that the first aid went through which may or may not solve the original problem. A few attempts have been made to create a standard hearing aid which fits most ears, however, the standard aid is normally round, oval or eliptical in shape so that it can fit either ear. The conical tip of such a standardized hearing aid often and frequently works its way out of the ear when the user eats, chews, yawns or talks.
Added to the complexity of providing a satisfactory hearing aid to a patient, are the various types of hearing losses which may occur. Because each patient may suffer a different type or frequency range of hearing loss the normal process includes hearing tests by an audiologist who then "prescribes" what the tester believes is the best correction which again may have to go back and forth between the factory until the specific hearing loss is matched with the characteristics of the electronics of the hearing aid. While it has probably been suggested that hearing aids could be massed produced for people with mild, moderate and severe hearing losses, due to the complexity of the hearing mechanism in the human body and patient individualities, such hearing aids could only be marginally effective for a limited number of individuals.
In-the-canal type hearing aids are made possible because of the miniaturization of batteries and necessary electronic components. These miniaturized components are incorporated into a single ear mold to be worn in the external ear, extending or penetrating into the auditory canal of a user. Locating the hearing aid in the ear, rather than on the belt or behind the ear, is preferred for acoustic reasons. The flap of the ear is shaped to be the primary sound gatherer of the human body. The crenulations of the ear are sound reflectors--they assist the brain in identifying the direction of the sound. The head, itself creates by diffraction, a shadowing of certain sound which also aids in such localization of sounds. Another advantage of this type of hearing aid is derived from its small size and, therefore, its inconspicuous cosmetic appearance. However, this advantage was previously thought to limit the production volume of in-the-canal hearing aids because miniaturization makes mass production and quality control difficult. Miniaturization has also limited the range of severity of hearing loss which can be effectively compensated for by in-the-canal hearing aids.
Generally, in-the-canal hearing aids are either individually fitted to the user's ear by a custom molding process (U.S. Pat. No. 4,471,490), or are selected from stock cylindrical canal aids having smooth polyvinyl surfaces (U.S. Pat. No. 3,852,540), usually constructed of a dental acrylic material (methylmethacrylate). Both of these methods have several disadvantages.
Individual fitting of the ear mold requires that an impression be made of the individual user's ear during a preliminary visit to the audiologist or hearing aid dispenser. The impression is sent to a craftsman for individual molding of the earshell to match the user's right and/or left auditory canals. These molds are then assembled with predetermined electronic components at the factory and fitted in the user's ears during a subsequent visit to the dispenser's office. In addition to the need for at least one subsequent visit, this method is uncomfortable because of the necessity of making an ear impression. The method is also expensive and time consuming due to the shipping, handling and individual craftsmanship required in production of each individual ear mold.
Selection of prior stock canal aids did not achieve an accurate fitting with the individual auditory canal of the user. Because stock canal aids conformed to standard requirements used in mass producing these aids, stock canal aids could not fit the individual shape of each auditory canal. The cylindrical or eliptical shape of the stock canal ads known in the prior art produced discomfort while wearing the hearing aid since it was not fitted to the individual ear canal. Also, the shape often resulted in the stock canal aid falling out of the ear since there was nothing in the shape that would "lock" the hearing aid into the ear canal.
The ear molds for stock canal aids of the past were manufactured in a cylindrical or eliptical shape so that the right and left ear molds were symmetrical and interchangeable. Recently, stock canal ear molds have added a single rearward bend to the basically cylindrical or eliptical shape of the ear mold shell. However, the same shell is still used for the right and left canals by inverting the shell before adding the cover plate. An oversized cover plate with the adjustable volume control and electronic components are attached to the shell. The periphery of the cover plate is then carved down and buffed to match the shell. The result is symmetrical right and left ear molds that are unique only because the volume control rotates in a different direction in the left ear mold than in the right ear mold.
In both custom in-the-canal hearing aids and stock canal aids, the formation of the ear mold by permanently attaching the cover plate to the shell creates serious problems in repairing and servicing these types of hearing aids. Since the electronic components are permanently sealed within the ear mold, the ear mold must be cut apart to service or replace any components which are defective. The replacement of defective electronic parts, for example, the microphone or receiver, may also alter the response characteristics of the hearing aid. Thus, servicing or repairing in-the-canal hearing aids, particularly including warranty repairs, is an expensive process which cannot typically be done at the hearing aid dispenser's store or office and which usually results in the hearing aid performing very differently after it has been serviced at the factory. In fact, warranty repairs are the single largest cost in the hearing aid industry, resulting from the patient's dissatisfaction with the prescribed and custom manufactured hearing aid.
Another drawback with both types of in-the-canal hearing aids known in the prior art is that the electronic components incorporated into these hearing aids are not specifically chosen by user selection. Currently, most manufacturers and hearing aid dispensers prescribe a certain combination of electronic components to be used in a hearing aid based upon the graphic results of the patient's audiogram. The audiogram chart shows the results of a hearing threshhold response or hearing acuity test performed by an audiologist or hearing aid dispenser using an audiometer. The audiometer consists of a pair of receivers placed in the user's ears, usually in the form of a headset, which are connected to a tone generating device. The operator varies the tones generated and inquires whether the patient can detect the generated tones at a variety of frequencies and amplitudes. The result of this process is that the hearing aid that the patient receives is not based on the patient's selected preference for a combination of electronic components. Rather, the components are usually selected from a prescription generated by the audiologist or hearing aid dispenser on the basis of the audiogram and/or the patient's response to the acuity tests.
Additionally, each manufacturer has its own method for interpreting the prescription and the audiogram into a specific combination of electronic components that are incorporated in the hearing aid. Complexity is added to the process because even the patient's own ear canal changes the prescription when the finished hearing aid is inserted into the patient's ear canal. This is due to acoustical "resonant" interactions between the ear canal and the characteristic sound output of the aid. The canal is a resonant chamber which will react differently to different frequencies for different patients. In addition, different standing wave patterns may develop for different patients depending on the frequency response of the aid and the patient specific spacing of the receiver and the patient's own eardrum, as well as ear canal geometry.
A few hearing aid dispensers use a master hearing aid device in an attempt to present simulations of different combinations of electronic components for a user to select among. With a typical master hearing aid, the user is given a set of headphones connected through the master hearing aid to an external microphone or external noise source. In a random manner the user is then asked to express a preference among the various simulated combinations. In practice, however, no master hearing aid achieves the goal of providing a hearing aid specifically chosen by user selection. Because a patient's hearing is tested on a device separate and distinct from the hearing aid eventually given to the patient, the characteristics of the device the patient tested with and the device the patient eventually receives are different.